Rechargeable solid polymer electrolyte battery cell

ABSTRACT

A rechargeable battery cell comprising first and second electrodes sandwiching a solid polymer electrolyte comprising a layer of a polymer blend of a highly conductive polymer and a solid polymer electrolyte adjacent said polymer blend and a layer of dry solid polymer electrolyte adjacent said layer of polymer blend and said second electrode.

The United States Government has rights to this invention pursuant toContract No. DE-AC02-76-CH00016, between the U.S. Department of Energyand Associated Universities, Inc.

This is a division of application Ser. No. 386,666 filed Sept. 6, 1982,now U.S. Pat. No. 4,442,185, which in turn is a continuation-in-part ofapplication Ser. No. 312,888 filed Oct. 19, 1981, now U.S. Pat. No.4,416,959, which in turn is a continuation-in-part of application Ser.No. 208,059 filed Nov. 18, 1980, now U.S. Pat. No. 4,352,868.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to photoelectric cells and methods oftheir manufacture, and more particularly to such cells employing dry,solid thin film polymer electrolytes and methods of their manufacture,as well as polymer films for use in such cells.

2. Description of the Prior Art

Photovoltage or the photovoltaic effect may be defined as the conversionof light or electromagnetic photons to electrical energy by a material.Becquerel in 1839 was the first to discover that a photovoltagedeveloped when light was shining on an electrode in an electrolytesolution. Nearly half a century elapsed before this effect was observedin a solid, namely in selenium. Again, many years passed beforesuccessful devices such as the photoelectric exposure meter, weredeveloped. Radiation is absorbed in the neighborhood of a potentialbarrier, usually a pn junction or a metal-semiconductor contact orjunction, giving rise to separate electron hole pairs which create apotential.

Photovoltaic cells have found numerous applications in electronics andaerospace, notably in satellites for instrument power, and poweringcommunications apparatus in remote locations.

Intensive research has been underway in the last decade to improve theproduction of these cells, e.g., (1) increasing the practical efficiencyin order to approach the theoretical efficiency, (2) decreasingproduction costs, and (3) to find new materials and combinations.

Interest in alternative energy sources and particularly in solar energyhas increased because of political and economic impetus. Traditionalsources of inexpensive energy are rapidly disappearing. Politicalinstability, price/supply fixing by certain governments, andenvironmental concerns, dictate the search for new energy sources. Thusthe present interest in solar energy. Each country has its own sunlightsupply, and the United States has an ample supply. Ecologically, solarcells are a non-polluting clean source of energy. Solar energy in ourforseeable future for many generations is limitless and non-depletable.One application of solar energy to which the present invention isdirected is the direct conversion of electromagnetic radiation,particularly sunlight, to electricity.

Two of the classical goals of any photovoltaic cell are efficiency, andhigher output voltage. Most prior art cells have a theoreticalefficiency of 25%. The cells of the present application approach 35%.The prior art voltage ranges from 0.2 to 0.5 volts per cell; theinventor's cells are approximately 0.625 volts.

Further, some prior art cells require that they be oriented so that theincident light is perpendicular to the face of the cell. In the presentinvention, while this is desirable, it is not essential, and they mayoperate at an angle from the perpendicular.

In the parent applications of which this forms a continuation-in-part,there is described in one embodiment a photovoltaic cell having asemiconductor layer and an adjacent polymer electrolyte. To improve theelectrical properties at the interface, there is included a conductivefilm between the semiconductor and the adjacent solid polymerelectrolyte. One of the objects of the present invention is to provide aconductive film that increases the interfacial contact area and improvesthe charge transfer characteristics between the semiconductor andpolymer electrolyte.

The present invention offers the possibility of ease of manufacture,attendant low cost, and manufacturing of large surface areas with goodquality and at a low cost.

The present invention is corrosion free. A reduction oxidation couple inwater has a competing photocorrosion reaction resulting from aninteraction between the water and semiconductors. The present inventionby using a polymer matrix avoids photocorrosion and the attendantproblems.

An object of the present invention is to provide novel, double andmultiple photoelectric cells for conversion of solar energy toelectricity.

Another object of the invention is to provide a method for themanufacture of double photoelectrochemical cells. A further object ofthe invention is to provide a half-double photoelectrochemical cell forthe conversion of solar energy to electricity using a thin film polymerelectrolyte, said polymer electrolyte being non-aqueous and solventfree.

A further object of the invention is to provide a new family ofphotoelectrochemical cells having a theoretical higher output efficiencyand output voltage than is available from single cells.

Another object of the invention is to provide cells which are easy tomanufacture and are stable in operation.

As noted in the parent applications, there is described a photovoltaiccell in which there is a thin film solid polymer electrolyte with asemiconductor adjacent thereto, and a conductive film between the solidpolymer electrolyte and the adjacent semiconductor. An object of thepresent invention is to provide an improved conductive layer thatincreases the interfacial contact area and the charge transfercharacteristics from the solid polymer electrolyte.

A further object is to provide a film of a polymer blend of a highlyconductive polymer and a solid polymer electrolyte, which can be usedfor electric cells.

A further object of the invention is to provide a method ofmanufacturing of conductive polymer electrolytes for use in electriccells.

These and other objects and features of the invention will be more fullyunderstood from the description of the embodiments which follow, but itshould be understood that the invention is not limited to theseembodiments and may find application as would be obvious to a manskilled in the art following the teachings of this application.

SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided a devicehaving a first layer of semiconductive material having a first band gap;and a second layer of semiconductive material having a different bandgap; a layer of dry solid polymer electrolyte between said first andsecond layers; and a layer of a polymer blend of a highly conductivepolymer and a solid polymer electrolyte between said dry solid polymerelectrolyte and said semiconductor layer.

According to another aspect of the invention, there is provided a methodof manufacturing such cells.

According to an aspect of the invention there is provided a thin filmproviding improved electric charge transfer across said film having apolymer blend of a highly conductive polymer and a solid polymerelectrolyte, said blend being the major component of said film at oneface thereof, and said dry solid polymer electrolyte being the majorcomponent of said film at another face thereof. Said blend of saidconductive and electrolyte polymer is more conductive than said drysolid polymer electrolyte.

According to another aspect of the invention there is provided a methodof manufacturing such film and device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a double photo-electrochemical cellaccording to the invention.

FIGS. 2 and 3 are band diagrams of the semiconductor elements of FIG. 1when the cell is without incident radiation, and when it receivesradiation, respectively.

FIG. 4 is a schematic diagram of a second embodiment of the inventionshowing a half cell.

FIGS. 5 and 6 are band diagrams of metal polymer semiconductor devicesof FIG. 4.

FIG. 7 is a band diagram of further embodiment of a cell having multiplejunctions in tandem.

FIG. 8 is a band diagram of an alternative embodiment of a cell havingmultiple junctions in tandem.

FIG. 9 is a schematic diagram of a further alternative embodiment of theinvention.

FIG. 10 is a band diagram of a modified cell.

FIG. 11 is a band diagram similar to FIG. 10, showing a furthermodification.

FIG. 12 is a diagram illustrating a method of manufacturing highlyconductive and transparent polymer films of the cells.

FIG. 13 is a schematic diagram of an alternative embodiment of theinvention.

FIG. 14 is a highly schematic detailed cross-sectional view of theregion of the polymer blend of FIG. 12.

The parent applications describe in at least one embodiment photovoltaiccells having a dry solid polymer electrolyte and adjacent semiconductorlayer. This invention, in one aspect, describes an improved contactbetween said solid polymer electrolyte and semiconductor. This improvedcontact uses a polymer blend of a highly conductive polymer, e.g.polypyrrole, and a solid polymer electrolyte, e.g. polyethylene oxidecomplexed with potassium iodide. This blend leads to an increase in theinterfacial contact area and an improved charge transfer characteristicbetween the electrolyte, and the semiconductor. It will be appreciatedthat there may be additional intermediate layers of conductors such asplatinum between the semiconductor and the blend. There is alsodescribed a method for manufacturing such a blend and the complete cell.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 there is schematically shown the photoelectrical cell havingtwo semiconductors, 1 and 2, separated by a polymer electrolyte 3.Incoming electromagnetic radiation, for example, sunlight, is shown byan arrow 4. Electrodes 5 and 6 are connected to the semiconductors 1 and2, respectively. The electrodes are connected by leads to a load shownhere as a meter 7.

Semiconductor 1 is a thin film of cadmium sulfide, CdS, n-type, and is athin film, approximately 1 micrometer thick. As shown in FIGS. 2 and 3,the n-type CdS has a wide band gap. Semiconductor 2 is a thin film ofcadmium telluride, CdTe, and is doped with a p-type impurity. The n-CdSis undoped and is balanced with more or less Cd or S. It is naturallyn-type due to vacancies in the structure of the material and cannot bep-type. The resistivity can be adjusted by the manufacturing process.The CdTe is doped p-type with phosphorous to a concentration of 1.3×10¹⁶cm⁻³. P-type CdTe has a narrower band gap than that of n-type CdS asshown in FIGS. 2 and 3. The two semiconductors 1 and 2 face each other,and are in contact with and separated by the thin film polymerelectrolyte 3.

The polymer electrolyte is an electron and or ion-exchange polymer, forexample, a polymer matrix containing a redox or reduction-oxidationcouple. The polymer matrix is a polyalkene oxide. Polyethylene oxide hasbeen tried and operates satisfactorily. Polyethylene glycol,polypropylene oxide, or polypropylene glycol also form suitable polymermatrixes. The redox couple is a polysulfide, e.g. polysulfide which hasbeen used by the inventor is Na₂ S₄. Concentration of Na₂ S₄ in theelectrolyte defined as a weight ratio, 0.25 grams of Na₂ S₄ for eachgram poly(ethylene oxide), or as the ratio of oxygen atoms in the chainto the metal cation, the O/Na⁺ ratio was 8. Nothing is known at thistime about the optimum ratio for maximum conductivity. Other couples maybe used. The polymer electrolyte film was made on the CdS 1 byevaporation from a methanol solution, i.e. polyethylene oxide with amethanol solvent. The thickness of the polymer film is about 10micrometers. Contact with the CdTe semiconductor 2 is by direct physicalcontacting and heating under vacuum with a pressure of 1 kg/cm².

Electrical leads shown schematically as 5 and 6 in FIG. 1 are connectedto the walls of the semiconductor films 1 and 2. The leads may be anyconvenient or conventional transparent electrical lead. If the incidentlight 4 falls on the semiconductor 1, then lead 5 is a grid, ortransparent electrode, at least for those portions of the spectrum whichare absorbed by the semiconductors 1 and 2. Lead 6 may also betransparent to permit light to enter from both sides of the cell.Alternatively, electrode 6 may be reflective itself or have reflectivematerial on the far side from the light 4, in which case anynon-absorbed radiation would be reflected and further absorbed.Electrodes 5 and 6 are connected to leads shown schematically and whichin turn are connected to a load, shown here as volt meter 7. A substrate(not shown) is provided as well as suitable mechanical protection forthe electrodes and semiconductors. The substrate and protective filmmust be transparent over that portion of the cell through which lightpasses. Glass is the usual substrate, although a plastic substrate in anencapsulation material may also be used. The electrode facing theincident light may have antireflection coating.

FIGS. 2 and 3 are band diagrams of the device of FIG. 1 FIG. 2 shows thedevice in the dark, and FIG. 3 the band diagram under illumination. Theband gap of n-type CdS is typically 2.4 eV. The band gap of p-type CdTeis typically 1.45 eV. At dark, the Fermi level E_(F) is the same in bothmaterials. Under illumination as shown in FIG. 3 with the incidentillumination shown schematically by the wavy line with the legend 14,the Fermi levels shift, and there is a net potential across thesemiconductors of V=E_(F) (n)-E_(F) (p). The two semiconductors havedifferent band gaps. There is thus a multi-color cell which divides thesolar spectrum into two parts, with the short wavelengths absorbed bythe wide band gap semiconductor 1, and the long wavelengths absorbed bythe narrow band gap semiconductor 2. The polymer electrolyte 3 permitsthe flow of charge there-across, and the two junctions 1-3 and 2-3 arein series. The maximum theoretical efficiency of the cell is about 35%.This can be compared with the best single junction photovoltaic cellcommonly used having a theoretical efficiency of 25%, that being forgallium arsenide. The theoretical efficiency of a cadmium telluride cellby itself is 25%; and that of a cadmium sulfide cell by itself is 16%.

The open circuit voltage measured by meter 7 reads 0.625 volts and ashort circuit current of 35 uA/cm² is obtained using 100 milliwatt/cm²Xenon light.

Semiconductors of all categories are applicable to the cell of thisinvention i.e. elemental semiconductors (e.g. silicon, germanium);II-VI; III-V; tertiary compounds (GaAlAs, InCuSe₂); layer compounds,transition metal dichalcogenides, (MoS₂, WS₂, MoSe₂, WSe₂); organicsemiconductors (e.g. 1000 A° phthalocyanines), polymeric semiconductors(e.g. polyacetylene). Single crystal, amorphous, or polycrystallinesemiconductors can be used. It is a matter of balancing goodsemiconductors with the right combination of (a) band gaps, (b) workfunctions, and (c) electron affinities in order to have the rightabsorption characteristics and to arrive at good rectifying junctions.

Determination of the resistances or the dopant concentrations at thisstage is a matter of optimizing the relative resistances in the cell,i.e. it depends on the resistance of the polymer film, which in turndepends on the polymer used. An average is somewhat higher than theresistances used in traditional photovoltaic cells, e.g. 10-50 ohm-cm.

Turning now to FIG. 4, there is shown an electrolytic Schottky barrierdevice or "half-cell" of the invention. In this embodiment there is anindividual junction. The embodiment of FIG. 4 is similar to the one ofFIG. 1 except that one of the semiconductors is replaced by a metal orcounter electrode 21. Electrode 21 is a thin metal film or grid which isa semi-transparent or other transparent counter electrode, e.g.tin-oxide or indium-tin-oxide, and is preferably completely transparentto that portion of the spectrum which is to be absorbed. Suitable metalsand oxides include Cr, Al, Cr/Cu alloy, Mg, Au, indium-tin-oxide, tinoxide. Layer 22 is either a p-type or an n-type semiconductor, and allsemiconductors are applicable. A polymer electrolyte 23 separates thetransparent counter electrode 21 and the semiconductor 22. A transparentcover for example, glass 25 or an antireflection coating is on anoutside face of the counter electrode 21. A conducting base electrode 26is on an outside face of the semiconductor 22. Light 24 passes throughthe transparent cover 25, transparent electrode 21, and electrolyte 23and is absorbed by the semiconductor 22. The device of FIG. 4 is anelectrolytic Schottky barrier cell and may have a higher open circuitvoltage than that of the solid state junction cells.

The band diagram of the device of FIG. 4 is shown in FIGS. 5 and 6 withn- and p-type semiconductors, respectively; and with light impingingupon the semiconductors. The flow and direction of holes, h⁺, andelectrons, e⁻, are shown in the semiconductor region. The voltage acrossthe electrodes 21, 26 at open circuit is V=E_(F) ^(semi) -E_(F) ^(metal)for the n-type semiconductor, and V=E_(F) ^(metal) -E_(F) ^(semi) forthe p-type.

The Schottky barrier `half-cell` may also be a backwall type cell, i.e.the light is incident on the semiconductor which is a thin film on atransparent conductive substrate. The counter electrode and the polymerin this case do not have to be transparent.

FIGS. 7 and 8 show two further embodiments of cells, both havingmultiple junctions in tandem. The cells discribed in FIGS. 1, 2 and 3are stacked in series and include more than two different band gaps.They may be independent cells connected in series with a transparentconductive substrate between the various cells as shown in FIG. 7; or,as shown in FIG. 8, the electrical contact may be made by furtherpolymer films.

In FIG. 7, there are shown four semiconductive thin films 71, 72, 73 and74. Films 71 and 72 are separated by polymer thin film electrolyte 75;and semiconductors 73 and 74 by electrolyte 76. A transparent conductiveelectrode 77 is spacer between semiconductors 72 and 73. Electrodes 5and 6 are connected to the outer face of semiconductors 71 and 74.Electrodes 5 and 77 are transparent conductive electrodes. 77 may be twoseparate electrodes connected in series. Incident light is shown, by thelegend hv, and the wavy arrow, falling upon electrode 5, and passingthrough the entire cell.

The band gap of the semiconductor 71 is greater than the band gap of thesemiconductor 72, which is greater than that of semiconductor 73, andgreater than that of 74.

E_(g)(71) >E_(g)(72) >E_(g)(73) >E_(g)(74) with hv incident on 71.

Polymer films 75 and 76 may be identical or different. The order of nand p types may, of course, be interchanged. The electrode 6 does nothave to be transparent.

Voltmeter 7 is shown connected to the electrodes 5 and 6, and thevoltage measured across that meter 7 is the sum of the potentials V₇₁,V₇₂, V₇₃ and V₇₄ developed across or by the semiconductors 71-74. FIG. 7is not to scale, and electrode 77 is shown in the figure of anexaggerated width in order to show the electrical levels between thesemiconductors 72 and 73.

FIG. 8 shows three semiconductive thin films 81, 82 and 83, separatedrespectively by two polymer thin films 84 and 85. The outer walls of thesemiconductors 81 and 83 have a transparent conductive film 5 and aconductive film 6 respectively. The band gap of semiconductor 81 isgreater than the band gap of semiconductor 82, which is greater than theband gap of semiconductor 83. Incident light hv impinges the transparentconductive electrode 5 which is connected to the widest band gap orfirst semiconductor 81 and passes through the array.

E_(g)(81) >E_(g)(82) >E_(g)(83) with light hv incident on 81

As in previous figures there is shown a voltmeter 7, connected to theelectrodes 5 and 6, and which measures the potential produced by thethree semiconductors so that V=V₈₁ +V₈₂ +V₈₃

Instead of NPP semiconductors the semiconductors may be PNN. The polymermatrix may be the same for polymers 84 and 85, but the molecular orionic species will be different; one producing a rectifying contact tosemiconductor 82, the other an ohmic non-rectifying contact. Forexample, film 85 makes ohmic contact, i.e. nonblocking contact, to thesecond semiconductor 82; and a rectifying barrier junction with thethird semiconductor 83. Semiconductor 83 has a larger work function thansemiconductor 82, if both are p type. The work function is defined asthe distance in energy between the vacuum level and the top of thevalance band of the semiconductor. If both semiconductors 82 and 83 aren-type, then semiconductor 83 must have a smaller electron affinity thansemiconductor 82. The electron affinity is defined as the distance inenergy between the vacuum level and the bottom of the conduction band ofthe semiconductor. Semiconductors 82 and 83 must be of the same type,for the flow of electrons to have the same sense in both semiconductors.Semiconductor 81 and semiconductor 82 are of the opposite type. Thesemiconductor 81 can be n-type or p type. The band gaps are arrangedaccording to E_(g)(81) is greater than E_(g)(82) which is greater thanE_(g)(83), where semiconductor 81 faces the incident light. The threelevel cell of the type shown in FIG. 8 has a theoretical efficiency ofapproximately 40 %, without concentration of sunlight.

Similarly, the number of cells is not limited to what is shown in FIGS.7 and 8, but more semiconductors may be added further in tandem toproduce multi-color cells of higher order. III-V compounds may beparticularly well suited for this type of manipulation of band gaps andelectron affinities.

A tandem cell may also be constructed by beginning with a Schottky cell,barrier cell, i.e. by substituting a transparent counter electrode forthe first semiconductor cell 71 in FIG. 7 or 81 in FIG. 8, and addingpolymer films followed by semiconductors as described above.

The cells described may also be used with systems which concentratelight onto a small area. The advantages of multicolor cells, or tandemcells, are even larger with concentrator systems. The efficiency of thecells is higher, and the added cost of producing the more complex cellsmay be offset by using cheap concentrator systems, e.g. plastic fresnellenses.

The higher efficiency is due to the following: As the number of cellsincreases, the photon flux available for absorption in any onesemiconductor in the stack decreases, which leads to a lowering of thephotovoltaic conversion efficiency of each junction. The total photonflux incident on the tandem cell stack can be increased by usingconcentrating mirrors and lenses, thus circumventing this efficiencyreduction.

The tandem cell concept is particularly compatible with solarconcentrator systems. It should be pointed out, however, that theefficiency of the stack still increases with the number of cellsrelative to the efficiency of a cell based on a single junction. Theproduction process may lead to inexpensive thin film tandem cells whichmay make concentrating systems economically unnecessary. Theefficiencies which are approximately 25% for 1 cell, 35% for 2 cells,40% for 3 cells are efficiencies calculated with no concentration, i.e.1 sun. For a concentration factor of a hundred, i.e. 100 suns, thecorresponding numbers are 30%, 42%, and 48%. The numbers vary somewhatdepending on the method of calculation but the trend is evident. Onereaches a limiting value of about 70% for an infinite number of cells.

An advantage of this invention is the ability to make the cells all thinfilm, (e.g. the thickness can be a few micrometers or less.) Singlecrystals may be used as well as amorphous or polycrystalline materials.The thickness of the semiconductor material depends on (a) theabsorptivity of the material (how thick to absorb all the light ofenergy above the band gap), and (b) the diffusion length (if light isabsorbed on the opposite side of the junction as in the CdS in theexample, the charges will have to diffuse to the junction region on theother side in order to be collected). For silicon, for example, thismeans a thickness of about 100 micrometers, and for GaAs or CdS, about2-3 micrometers.

The polymer film will be less than 1 micrometer thick, (even less than0.1 micrometer) depending on its resistivity and deformability.

Many redox couples can be used, e.g., I⁻ ₃ /I⁻, TCNQ⁻ /TCNQ. These redoxspecies with a single charge can be transported as ions through thepolymer. Ions with multiple charges may interact too strongly with thematrix to have ionic mobility but at high concentrations may provideelectronic conductivity by hopping or tunneling between the molecules.In this case, applicable multiple charged redox species include e.g.Fe²⁺ /Fe³⁺, Fe(CN)³⁻ 6/Fe(CN)⁴⁻ ₆, Quinone (Q/QH₂), and others.

Polymers to be used can be grouped in five catagories.

(i) For solution produced films, insulating polymers with highdielectric constants and therefore high solubility for ions areapplicable for the production process described. Polymers with sulfonicgroups are good, i.e. sulfonic polymers.

(ii) Electronically conductive polymer films with ions dissolved in thepolymers, e.g. polyacetylene. The combination of electronic and ionicconductivity imparts higher mobility to the ionic species in order topreserve space charge neutrality in the film. There is at the momentongoing research with the aim of using polyacetylene for ion transport.This is essentially a new use of a new class of polymers.

(iii) Poly(phenylene oxide) incorporating ferrocene. These films areproduced by electrochemical oxidation on metal surfaces. They may beproduced on the transparent counter electrode. Then the semiconductormaterial is placed on top of the polymer, n- or p-type. Alternatively,the doped polymer may be produced directly on the surface of an n-typematerial by the process of photo-electro-oxidation by illuminating withlight having energy higher than the band gap of the semiconductor. Ananodic (positive) polarization is applied to the semiconductor in orderto drive the minority carriers (holes) to the semiconductor/electrolyteinterface to perform the oxidation of the monomer in solution topolymer, which deposits onto the semiconductor surface. The polymeritself is insulating. Molecules can be incorporated into the polymermatrix from the same solution. The resulting polymer film is uniformlydoped with molecules or ions and therefore forms a rectifying barrierwith a semiconductor. This process is applicable to other insulatingpolymer matrices than poly(phenylene oxide) and to other dopants thanferrocene. An example of this process for a different type of polymer,is the electronically highly conductive polymer of polypyrrole.

An equivalent process is photo-electroreduction on the surface of p-typesemiconductors. The absorbed light of energy larger than the band gap ofthe semiconductor produces electron-hole pairs. Cathodic(negative)polarization on the semiconductor makes the minority carriers(electrons) flow to the semiconductor/electrolyte interface and can beused to reduce monomers in solution to polymers on the surfaceincorporating dopant molecules or ions from the solution. The process isthus a one-step oxidation or reduction and doping. An example of thisprocess is the electrochemical reduction of acrylonitrile topolyacrylonitrile.

The polymers which can be photoelectropolymerized on n-typesemiconductors in the manner described above can be polymerised onp-type semiconductors as well by anodic polarization without light.Similarly, the polymers which can be photoreduced on p-typesemiconductors can be reduced directly by a negative voltage on thesurfaces of n-type semiconductors.

(iv) Polymers with pendant groups attached to the backbone of insulatingpolymers, e.g. TTF substituted polystyrene copolymer. The energy levelswhich interact with the semiconductor to produce a junction are definedby the pendant molecules which, in high concentrations, produceelectronic conductivity by hopping or tunneling. These energy levels canbe adjusted by substituting different pendant groups.

(v) Various polymer production techniques may be used, including (i)Solvent evaporation:(spin-coating is used to produce thin uniform films.This has been used with pendant group polymers and with poly(ethyleneoxide). (ii) Glow discharge polymerization. (iii) Oligomerization duringsurface chemical reaction. (iv) (Irreversible) adsorption of polymerfilms. (v) Plasma polymerization. (vi) Electrodeposition, and (vii)Functionalization of surface bound polymers. Several techniques may becombined either at the same junction or at successive junctions.Poly(ethylene oxide), for example is soft and a very thin coating maynot have the rigidity required for assembly. A very thin layer of a morehighly conductive polymer is photoelectro-polymerized on a face of oneor both of the semiconductors and a soft material e.g. poly(ethyleneoxide) is between the two.

Techniques for producing semiconductor thin films include thesetechniques for making the semiconductor film directly on top of thepolymer film, which has been made on a transparent electrode or theopposite semiconductor. They include (i) Spray pyrolysis (solutionspraying). This requires substrates held at elevated temperatures,sometimes up to 400° C., and requires polymers which can withstand suchhigh temperatures. (ii) Silk screening (seriographic) techniques. (iii)Deposition from aqueous solution. Solution of ions precipitate assemiconductor films on top of the substrate. This has been demonstratedfor a number of II-VI compounds, e.g. CdS, CdO, ZnO, and is not a hightemperature process. (iv) Cathodic codeposition of different elementsusing the polymer coated electrode as cathode. This has beendemonstrated for CdSe (without polymers on the electrodes). It involvesan aqueous solution and is therefore not a high temperature process. (v)Anodic formation of semiconducting films by using the polymer coatedelectrode as an anode in aqueous solution. This has been demonstratedfor CdS and Bi₂ s₃. This is not a high temperature process.

FIG. 9 shows an alternative embodiment of the cell of this invention.Two semiconductor films 91 and 92, for example, n and p typerespectively, are separated by a thin film electrolyte 93, e.g., apolyethylene oxide redox couple. On one, or both sides of the film 93,there is a highly conductive polymer 94. In FIG. 9, the highlyconductive polymer 94 is shown on both sides, however, it need not be onboth. The film 94 is a highly conductive polypyrrole doped with asuitable transport ion, for example, BF⁻ ₄ or ClO⁻ ₄. Other filmsinclude polyphenylene-oxide doped with ferrocene; or polyphenylenesulfide doped with ferrocene. Alternatively, the films 94 may be a thinfilm metallic layer, for example, gold, silver, or platinum. In the caseof the highly conductive polymer, the film is several hundred angstromsthick. If the film is metallic, it is a few angstroms to a few hundredangstroms thick. The conductive polymer film 94 on either side of thefilm 93 may be the same or of different types. The film 94 has a workfunction such as to make a rectifying energy barrier within thesemiconductor. Of course, the thin films 93 and 94 must be transparent,and that controls the maximum thickness.

One may view the embodiment of FIG. 9 as at least one semiconductor witha highly conductive film 94, adjacent to which and together with is thefilm 93 and the other half of the tandem or multiple cell.

In all the cells of all the figures the polymer electrolyte is notlimited to ion conductors, but any polymeric conductor is suitable, solong as it be capable of conducting electricity and is not limited tothe ionic ones. This is sometimes termed any solid polymer electrolyte.

In FIG. 9 it should be noted that the Fermi level in the band diagram ofthe layers 93 and 94 is constant and does not shift in both the dark andunder illumination. Of course the Fermi levels in the two semiconductors91 and 92 do shift during illumination, and this of course produces thevoltage across the cell.

An example can be given of the formation of highly conductingpolypyrrole on the surface of n type silicon. The method is applicableto other combinations of polypyrrole and polymers on semiconductormaterials.

Pyrrole can be polymerized onto the surface of metal electrodes anddoped to a conductive form by a one-step electrolytic oxidation ofpyrrole in acetonitrile solution using a tetraethylammoniumtetrafluoroborate electrolyte. Dark electrolytic oxidation on an n-typesemiconductor is impossible because the oxidation potential of pyrrolelies at a higher positive potential than the flat band potential or theconduction band edge of the known semiconductors. The oxidation ofpyrrole to polypyrrole on an n-type semiconductor surface is carried outby illuminating the semiconductor with light of an energy higher thanthe band gap and applying a small anodic bias. The minority carriersgenerated by the light absorption migrate to thesemiconductor-electrolyte interface where they oxidize the pyrrole whichin turn deposits onto the surface as polypyrrole. The polymer isuniformly doped by anions from the electrolyte to a highly conductiveform or a p-type semiconductor depending on the solution concentrationof the dopant. It is produced on single crystal, polycrystalline, oramorphous semiconductors.

FIG. 10 is a band diagram, (Similar to FIG. 5) of a modification of thecell of FIG. 4, to improve the rectifying junction between semiconductorand electrolyte.

The doping in the semiconductor is varied in order to produce asemiconductor surface layer of higher resistivity than the polymerelectrolyte. An n-type semiconductor would have the designation n/n⁺which denotes a layered structure of a lightly doped film (n) on top ofa more heavily doped substrate (n⁺) of the same material. Examples oflightly doped are 10² -10⁶ ohm-cm and heavily doped 0.01-10 ohm-cm. Thethickness of the lightly doped layer is as thick as a few micrometers(2-3 μm) or as thin as 1000 Angstroms. This structure also provides aback surface field to help in the separation of the charges.

In FIG. 10, the electric fields are represented as slopes of the energybands of the semiconductor. The back surface field has the samedirection as the field at the interface, and thus aids in the chargeseparation for that part of the light which is absorbed further into thesemiconductor.

For p-type semiconductors the structure would be p/p⁺, exactlyequivalent.

The resistive surface layer may be made epitaxially on the moreconductive substrate. If the semiconductor is a film (e.g. made byevaporation or sputtering), the dopant concentration may be varied byvarying the rate of evaporation from the dopant source. If thesemiconductor is made by electrolytic deposition, the dopantconcentration can be varied by changing the dopant concentration in theelectrolyte.

The counter electrode is transparent and can be a thin metal film onglass (e.g. Au, Pt, Pd, Co) 50-150 Angstroms thick, a conductive oxide(e.g. indium-tin-oxide or tin-oxide), or a conductive oxide with a verythin metal film to enhance the charge transfer capabilities (e.g. 5-100A of Pt, Pd, Au, Co).

This structure has a higher resistivity in the semiconductor surfacelayer than in the electrolyte. Thus the built-in voltage across thejunction falls across the semiconductor rather than the electrolyte.This electric field across the surface layer of the semiconductor isnecessary for efficient separation of the photogenerated charges.

FIG. 11 is a band diagram (similar to FIG. 10) of a further modificationof the cell of FIG. 9.

A rectifying junction is made by depositing a transparent, highlyconductive film 111 on the surface of the semiconductor. The film can bea highly conductive polymer (e.g. polypyrrole) or a metal (e.g. Pt, Au).For an n-type semiconductor substrate the material must have a high workfunction (electronegativity) and for a p-type semiconductor the materialmust have a low work function (electronegativity) in order to make arectifying junction with the semiconductor. The thickness of the polymeris typically 100-1000 A and for the metal 5-150 A.

The n/n⁺ structure of FIG. 10 may be employed in addition to the surfacemodification. The situation for a p-type semiconductor is exactlyequivalent.

It is advantageous to modify the surface with a very thin film of metal(e.g. Pt) of 2-3A to 50A thickness before depositing the polymer,especially when using n type Si with polypyrrole deposited from aqueouselectrolyte.

The double cell of FIG. 1 may include the modification of FIGS. 10 and11. In FIG. 1, the (modified) semiconductor replaces the counterelectrode, the second semiconductor will be of different band gap thanthe original and of opposite type, light being incident on the back sideof the wide band gap semiconductor which has a transparent ohmic(non-rectifying) contact. Similarly, the modifications of FIGS. 10 and11 may be applied to the cells of FIGS. 7 and 8.

FIG. 12 is a diagram illustrating method of manufacturing highlyconductive and transparent polymer films; for example thephotoelectrochemical generation of thin conductive polymer films (e.g.polypyrrole) on n-type semiconductor (e.g. n-Si) using light absorbed bythe semiconductor.

A semiconductor 120 is immersed in a solution 121 which contains themonomer (the building blocks of the polymer chain) and a supportingelectrolyte which contains the species to be used as dopant for thepolymer. The light is absorbed by the semiconductor, and generateselectron-hole pairs (h⁺, e⁺). A positive potential from a source 122 onthe semiconductor drives the holes to the semiconductor-electrolyteinterface. The hole reaching the interface takes an electron from(oxidizes) a monomer in the solution. A polymer film wil then grow bythis electro-oxidation process on the surface of the substrate.Electro-oxidation has been known on metal surfaces (where light is notneeded) for a number of different polymers (see list at the end of thissection). The process is used for polypyrrole, polyaniline andpolythienylene on semiconductors. Exactly how the process occurs on themolecular level is not yet known.

The monomer concentration (e.g. pyrrole) is typically 0.01 Molar to 1.0M, the supporting electrolyte contains the ions to be used as dopants(e.g. BF⁻ ₄, ClO⁻ ₄, I⁻, Br⁻, Cl⁻) typically in concentrations 0.01-1.0M. The dopant molecules (e.g. BF⁻ ₄) will be included in the film as itis being made. The dopants will be acceptors (of electrons).

The doping may also be done from the gas phase of the dopant. It mayalso be done electrochemically after the film is made.

The solvent is an organic solvent (e.g. acetonitrile, dimethylformamide,dimethylsulfoxide, propylene carbonate, methanol) or water. It may alsobe a mixture (e.g. acetonitrile+pyridine).

The doping and the manufacturing of the polymer films may thus be aone-step process. The polymer films will continue to grow only as longas the light is on and the film is not yet thick enough to absorb allthe incident light. Thick films become black and non-transparent becausethey are highly conductive.

A negative potential on an illuminated p-type electrode drives thephotogenerated electrons to the interface where they reduce (add anelectron to) a monomer species in solution which then builds a polymerfilm on the surface of the semiconductor. The dopant in this case willbe an electron donor (e.g. Na, K).

Several films can be made in the same manner:

Polyaniline

The monomer is aniline, the concentrations and the solvents and theprocedures are the same.

Substituted Anilines. ##STR1## R₁ -R₅ each are a member of the followingchemical groups: para-CH₃, para-OCH₃, ortho-CF₃, meta-CF₃, para-COOH,ortho-NH₂, para-NH₂.

Other substituents are also applicable. e.g. p-toluidine, p-anisidine,2-aminobenzotorifluoride, 3-aminobenzotrifluoride, p-aminobenzoic acid,p-phenylenediamine, and o-phenylenediamine. In the case of aniline, theparent compound, all the R₁ -R₅ are H, hydrogen.

Polyphenylene oxide (PPO) ##STR2## R₁ -R₅ can be hydrogen or substituentgroups. Dubois et al. have studied alcohol substituents, alkyl radicalsubstituents, hydroxy-or carboxymethylated groups (ref. 4).

The medium is e.g. Methanol--0.15 Molar NaOH containing 0.2 Molarconcentration of the monomer to be polymerized. In principle the samesolvents and concentrations as well as the dopants used with theanilines and pyrrole are applicable. There is higher electricalconductivity when the ferrocene is in the solution.

Poly(2,5-thienylene) (or polythiophene)

The monomer is thiophene which can be polymerizedphotoelectrochemically. ##STR3##

Certain polymer films can be made by condensation from the gas phase,e.g. (SN)_(x) or polysulfurnitride, where the (SN)_(x) source is held at135-150 degrees centigrade and the surface to be polymerized at 15°-20°C.

Other polymer films can be made by gas phase ionization or plasmapolymerization, by an electric discharge in a gas of the monomer.

The thin transparent metal films are made as follows: If thesemiconductor surface is modified by a metal film the film can be madeby deposition in vacuum (thermal evaporation or sputtering) orelectrolytically from a solution containing ions of the metal to bedeposited. The thickness of the metal film can be from 2-3 Angstroms to150 Angstroms. The metals traditionally used have been Pt, Pd, Au, Mg,Cr, Al, Cs, Cr-Cu alloys. Metal oxides which have been used includeindium-tin oxide and tin indium-tin oxide, tin oxide.

The polymer electrolyte used is an electron or ion exchange polymer,e.g., a polymer matrix containing a redox reduction-oxidation couple,and includes:

1. Polyethers: polyethylene oxide and polypropylene oxide.

The films are cast from solutions containing dissolved redox couples,e.g., iodine (I⁻ ₃ /I⁻), bromine (Br⁻ ₃ /Br⁻), tetracyanoquinodimethane(TCNQ⁻ /TCNQ), and polysulfides (e.g, all of which) are good candidatesfor ion exchange couples.

More speculative are iron (Fe²⁺ /³⁺), ferricyanide (Fe(CN)₆ ^(3-/4-)),and Quinone (Q/QH₂). These are multiply charged and may not transportthrough the matrix. However, at high concentrations they may conduct viaelectron hopping.

2. Polyurethanes made from polyethylene glycol and polypropylene glycol.

3. Polyacetylene.

4. Polyhydroxyphenylene which conducts via electrons and ions and fallsin the same category as polyacetylene.

5. Polymers with electroactive groups attached to the polymer backbone,e.g. phenoxytetrathiafulvalene. Tetrathiafulvalene (TTF) groups areattached to the polystyrene backbone. This polymer is a very good mediumfor transporting ions. Polystyrene itself is an insulator. Attachingother groups than TTF changes the charge transfer properties and allowsfor possibly optimising the ion exchange polymer, i.e. different groupscorresponding to different redox energy levels, which in turn arematched with the semiconductor energy levels.

6. Polysulfone. This is a substitute for the polyethers.

7. Cellulose acetate.

8. Poly(gamma 8-methyl L-Glutamate).

Semiconductors of all categories are applicable to the cells:

1. Elemental semiconductors: Si, Ge

2. II-VI compound semiconductors (from the columns II and VI in theperiodic table): Cadmium sulfide (CdS), Cadmium Telluride (CdTe), CdSe,ZnSe, ZnTe.

3. III-V compounds: GaAs, GaP, InP, AlAs, AlP.

4. III-V ternary alloys: GaAlAs.

5. Tertiary compounds: CuInS₂, CuInSe₂.

6. Transition metal chalcogenides: WS₂, WSe₂, WTe₂, MoS₂, MoSe₂, MoTe₂,ZrS₂, ZrSe₂, etc.

7. Other inorganic semiconductors: Bi₂ S₃, Zn₃ P₂, CuO, CuS₂.

8. Organic semiconductors: anthracene, tetracene, pentacene, etc.

9. Pigment films: Cyanines, phthalocyanines, hydroxysquarylium etc.

10. Polymeric semiconductors, e.g., polyacetylene, polyacrylonitrile.

Single crystals, polycrystalline, and amorphous films, in particularamorphous Si, are all applicable. Dopant concentrations will beoptimized for each particular interface.

Thus, there has been shown and described several novel photovoltaiccells using solid polymer electrolytes. Polymer electrolytes are a newconcept in photoelectrochemical cells for the conversion of solar energyto electricity. It is envisioned that this is a basic invention of suchdevices and the invention should not be narrowly interpreted during thelife of any patent. Those following the teachings of this applicationwill no doubt be led to other and additional polymer electrolytes andother semiconductors than those specifically described herein (which arethe ones that have been employed by the inventor in his research todate).

FIG. 13 is similar to FIG. 9. It shows an n-type semiconductor 131, ap-type semiconductor 132, a dry solid polymer electrolyte 133, and ahigh conductive layer 134. The layer 134 increases the interfacialcontact area and between the semiconductor 131 and the adjacentelectrolyte 133, and also produces an improved charge transfercharacteristic at this interface and of the whole device. The highlyconductive layer 134 is a polymer blend of a highly conductive polymer,e.g. polypyrrole and a solid polymer electrolyte, e.g. polyethyleneoxide complexed with potassium iodide. In the blend 134, the polymerelectrolyte component penetrates into the conductive polymer component133 resulting in increased contact area, and thus better charge transferacross the interface. The film 133 is for example, several hundred to10,000 angstroms thick; and layer 134 is 100 to 1000 angstroms thick.Both layers are essentially transparent.

The polymer blend 134 is synthesized directly on the surface of thesemiconductor 131 by a technique of photoassisted electrochemicaloxidation from a solution of the monomer of the highly conductivepolymer and the polymer electrolyte in its complexed form. The resultingpolymerization of the highly conductive polymer, e.g. with the complexedpolymer electrolyte present in solution produces a polymer blend of thetwo polymer phases

A method of manufacturing the basic cell is as follows, with theimproved blend. The semiconductor 131 may be coated with a thin layer ofplatinum, e.g. 5-50 angstroms. This is particularly desirable where then silicon is single crystal. The platinum layer may be provided e.g. byvacuum evaporation, or electrolytic deposition. The platinum layerproduces a better electronic and physical coupling between thesemiconductor and the polymer and thus leads to better charge transfer.If the semiconductor layer 131 is amorphous or polycrystalline silicon,then the platinum may also be used. The semiconductor may be any ofthose listed previously in the specification, for example CdSe, CdTe,and CdS. If the layer 131 is p-type silicon, a low electronegativitymetal may be used, e.g. indium or aluminum.

A solution is formed containing (i) acetonitrile as solvent, (ii)Et,NBF, (tetraethylammonium tetrafluoroborate), (.e.g 0.01-1.0 Molar),(iii) Pyrrole (0.01-5.0 Molar), (iv) 0.01-3.0% PEO by weight; molecularweight of PEO may be 10⁴ -5×10⁶ ; (v) KI in a ratio of 4.5-8 polyetheroxygen atoms per potassium atom, and (vi) I₂ in a ratio of KI:I₂ =4:1.The substrate 131, with or without the platinum layer, is immersed intothe solution and the semiconductor is held at 0.5 volts or higherpotential, versus the standard calomel reference electrode.

The member 132 in FIG. 13 of the completed cell may be another p-typesemiconductor, or a counter electrode comprising glass with atransparent conductive coating, e.g. indium tin-oxide (ITO), orplatinum, or chromium, or other material as mentioned previously. Thecounter electrode may be coated, especially when it is ITO, with a thinlayer of platinum, e.g. 5 to 50 angstroms for better charge transfer tothe solid polymer electrolyte. When ITO is the counter electrode, theplatinum is needed because ITO is an insert electrode with the iodineredox couple.

The element 132, whether a counter electrode on a glass support, or asemiconductor, or a web filled with charge carriers, (1) may be coatedwith platinum or chromium or other metal layer; or (2) may have a blendof polymer of a type described herein in place of such metal layer; or(3) may in addition to the platinum or other metal layer, have a layerof polymer blend on top.

Once the semiconductor layer 131 has been formed with the polymer blend,and the right hand member 132, prepared (whether bare, or with a layerof metal and/or a layer of polymer blend on the face thereof); the nextstep is to form the dry solid polymer electrolyte 133. A film ofpolyethylene oxide complexed with, (or doped with), potassium iodide andiodine is solution cast by solvent evaporation from acetonitrilesolution, for example, by spin coating. The thickness when dry is in therange of 0.01 to 1.0 microns. The polymer electrolyte may be formed onthe polymer blend film 134, or on the surface (bare or prepared) ofelements 132 or on both. The two halves of the cell 131--134 and 132 arethen contacted to each other by heating to 70°-100° C. under vacuum withpressure about 1 kg/cm² for ten minutes to ten hours.

Thus, it will be appreciated that the dry solid polymer electrolyte 133is adjacent to the polymer blend 134 (which is a composite of dry solidpolymer electrolyte with the highly conductive polymer). During the stepof forming the polymer blend 134, there was an electrochemicalpolymerization of polypyrrole in a solution containing PEO-KI/I₂.Polyethylene oxide is a polymer soluble in acetonitrile. As thepolypyrrole film grows, it entraps the PEO-KI/I₂ phase within it,resulting in a polymer blend of polypyrrole and PEI-KI/I₂.

A modification of the method just described may be achieved by using adifferent complexing salt for PEO. The reason is to avoid two competingpaths for the current to flow:

(i) polymerization of pyrrole (2.2-2.4 electrons per pyrrole monomer).

(ii) oxidation of the iodide in the electrolyte solution, i.e. 2h⁺ +3I⁻→I₃ at the semiconductor surface 2e⁻ +I₃ ⁻ →3I⁻ at the counterelectrode, where h⁺ designates a hole and e⁻ designates an electron.

Reaction (ii) is a parasitic reaction which lowers the yield of thepolymerization. This may be improved as follows:

(a) Polymerize from a solution of what has been previously describedplus PEO complexed with KNO₃, (alternatives are NaNO₃, KCl, NaCl, KClO₄,NaClO₄, NaBF₄, KBF₄). NO⁻ 3 and the other anions are not electroactiveat the potentials in question and should not therefore contribute aparasitic current.

(b) Upon contacting the polymer blend of polypyrrole and PEO with a filmof PEO-KI/I₂ an electrochemical exchange of anions will automaticallytake place giving a polymer blend of polypyrrole and PEO KI/I₂, i.e. theNO₃ will diffuse out of the blend and the iodide will diffuse in. FIG.14 is an enlarged highly schematic view of the cross-section showing theblend. This is an artistic representation of what is believed the blendlooks like, with long strands of polypyrrole extending outward from theplatinum layer 135. Like elements in both figures bear like legends.

Various alternatives may be used, some of which are indicated above inthe specification. An alternative material for the dopant is NaI for KI;alternative materials for the highly conductive polymer includepolyindole, polyazulene, polythiophene and polyfuran; and for the solidpolymer electrolyte, polypropylene oxide for PEO.

An electric battery cell can also be constructed in which polyacetylenesuitably doped is used in place of the semiconductor 131 and 132. Dopingfor example is with sodium and iodide ions. A Polyethyleneoxide solidelectrolyte is used, and the polymer blend at one or both faces of thePEO is polyacetylene-polyethylene oxide. An alternative cell is withdoped polyparaphenylene as elements 131 and 132, doped PEO as polymerelectrolyte and a blend of polyparaphenlene and polyethylene oxideformed at the interfaces between the polyparaphenylene and polyethyleneoxide.

Thus, there has been described an improved cell having increase ininterfacial contact area and improve charge transfer characteristics dueto the polymer blend between the solid polymer electrolyte electrodes,and the adjacent counter electrode and or semiconductors.

I claim:
 1. A rechargeable battery cell comprising a first electrode; apolymer blend of a highly conductive polymer and a solid polymerelectrolyte adjacent said first electrode; a dry solid polymerelectrolyte adjacent said polymer blend; and a second electrode adjacentto said dry solid polymer electrolyte.
 2. A cell according to claim 1,wherein said second electrode comprises a second layer of polymer blendof a highly conductive polymer and a solid polymer electrolyte, and ametal electrode.
 3. A cell according to claim 2, wherein said polymerblend comprises a highly conductive polymer selected from the groupcomprising polypyrrole, polyindole, polyazulene, polythiophene,polyfuran, polyacetylene, and polyparaphenylene.
 4. A cell according toclaim 3, wherein said dry solid polymer electrolyte comprisespolyethylene oxide or polypropylene oxide complexed with NaI, KI or LiI.5. A cell according to claim 2, wherein said dry solid polymerelectrolyte comprises polyethylene oxide or polypropylene oxidecomplexed with NaI, KI or LiI.
 6. A cell according to claim 1, whereinsaid polymer blend comprises a highly conductive polymer selected fromthe group comprising polypyrrole, polyindole, polyazulene,polythiophene, polyfuran, polyacetylene and polyparaphenylene.
 7. A cellaccording to claim 1, wherein said dry solid polymer electrolytecomprises polyethylene oxide or polypropylene oxide complexed with NaI,KI or LiI.